The trunk of a small fir tree in my garden broke, and the tree fell over. More in hope than expectation I pulled the top part back up, taped the halves back together, and screwed in metal plates to hold them in place.

To my amazement the tree survived and, months later, when I removed the tape and the plates, the break had healed and the trunk was whole again. How do trees repair such trauma? Can all tree species do it?

Alan Crowther, Birmingham, UK